The present invention relates to radiation-curing coating systems, a process for their preparation and their use.
Radiation-curing coating systems are used to coat surfaces of wood, metals and plastics.
In some formulations the known radiation-curing coating systems have the disadvantage that the surface hardness is inadequate.
It is therefore an object of the present invention to develop radiation-curing coating systems which do not have these disadvantages.
The above and other objects of the present invention can be achieved by radiation-curing coating systems, which are characterized in that they comprise at least one silanized silica, where a silane from the group consisting of hexamethyldisilazane, 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane is used as the silanizing agent.
In a preferred embodiment of the invention, the silanized silica can be structurally modified. A silica such as described in the document EP 0 808 880 A2 can be used as the silanized silica. This document is incorporated herein by reference. The silica according to EP 0 808 880 A2 is a silanized silica with the following physico-chemical properties:
This silanized silica is prepared by a process in which a silica is sprayed optionally first with water or dilute acid and then with a surface modification reagent or a mixture of several surface modification reagents in a suitable mixing vessel, with intensive mixing, the components are re-mixed for 15 to 30 minutes and heat-treated at a temperature of 100 to 400xc2x0 C. over a period of 1 to 6 h, and the silanized silica is then destructured/compacted by mechanical effects and re-ground in a mill.
A silica prepared pyrogenically by the route of flame hydrolysis of SiCl4 can preferably be employed as the silica. Hexamethyldisilazane, for example, can be employed as the surface modification reagent.
The coating according to the invention which can be cured by radiation comprises a reactive binder which contains double bonds in the terminal position or in the xcex2-position relative to a reactive group which can be polymerized by free radicals. The double bonds can cure or polymerize under the influence of UV light or electrons. Copolymerizable reactive thinners (monomers) can be used to lower the viscosity.
Further components can be fillers, flatting agents and/or pigments. If required, wetting agents, flow control and degassing agents and other additives can be used in radiation-curing systems.
In UV technology, photoinitiators or photosensitizers are used to initiate the polymerization. In the case of curing by electron beams, the high-energy radiation itself forms the initiator radicals for the polymerization reaction.
The invention also provides a process for the preparation of the radiation-curing coating systems according to the invention, which is characterized in that 1 to 20%, preferably 2 to 10% of silanized pyrogenic silica, depending on the rheology of the system, is stirred into the coating system.
The coating systems according to the invention can be used for coating a wide variety of surfaces such as derived timber boards, solid wood, wood veneers, parquet, decorative papers, decorative films, thermoplastics and thermosetting plastics, mineral and polymeric glasses, metals (for example aluminium, high-grade steel, phosphated, chromated and galvanized steel sheets, copper), lacquered surfaces, surfaces coated with printing inks and leather.
The radiation-curing coating systems according to the invention have the following advantages:
Improvement in the surface hardness, in particular scratch resistance, without impairment of the application properties, and in the optical properties of the crosslinked coating films.
According to the invention, the pyrogenically prepared silicas according to table 1 can be employed as the silica for the silanization.
Physico-chemical Data of Aerosil